1. Field of the Invention
This invention relates to a method of preparing crystalline aluminosilicate catalysts of for example the ZSM-5 type, having carbon deposited within its pores. Catalysts so prepared have improved steam stability and are highly active in catalytic conversions of oxygenated hydrocarbons such as methanol to olefinic products.
2. Description of the Prior Art
The deleterious effect of steam on zeolites has been the subject of numerous papers and patents. This irreversible damage and loss of catalytic activity is thought to occur from hydrolysis of tetrahedral aluminum from the framework of the zeolite.
It is believed that this is the first instance in which a freshly synthesized aluminosilicate zeolite catalyst has been stabilized against steam deactivation by converting substantial amounts of organic carbon and/or a suitable charring agent adsorbed therein to a carbonaceous deposit within the pores of the zeolite. Coking of catalysts is a known phenomenon and is usually thought to be undesirable because it deactivates the catalyst. Therefore, the desirability of retaining carbonaceous deposits within the pores of a catalyst for the purpose of improving the steam stability of the catalyst is in applicants' view a surprising and unexpected discovery. Apparently the presence of coke prevents the hydrolysis of framework aluminum and the loss of protonic sites thereby suggesting that carbonaceous materials adsorbed on active sites serve to protect the aluminum lattice sites from the abovereferred to hydrolysis.